Hi johnro79
yes on a 2012 A6 , as I said I did it with out removing the headliner , removing the rear reading light cluster was the easy bit , had a mate to gently pull the roof liner in a downwards direction so I could undo the bolt that held the antenna to the roof, also put a block of wood between the roof liner and roof when my mates arms got tired , just fiddly. Roof went back with no sagging - all good.
In my opinion the aerials are not sealed properly, I took mine apart (see pic six tiny "star" screws ) and it was corroded inside.
also if you buy from the dealer they come in Matt grey , the dealer offered to paint it for me - I declined! All you have to do is take the old one apart and the new one and swap the "shark fin" cover job done.
**IMPORTANT**** , When you swap the covers , put a bead of silicone sealant around the edge on the inside of the antenna then screw the cover back on , then another thin bead on the outside of the aerial along the join to prevent dampness/ water ingress.
Make sure you get the right antenna , I have SIM card in the dash so the aerials might be differant if you don't have this - I'm sure someone will chime in amd point you in the right direction.
Aerial from dealer was £90.00 delivered
OR CHEAPER EASY FIX (this will sort the satellite side of things but not the mobile signal , but your aerial may not have the "mobile bit" ?
Go to eBay , search for "Trimble GPS " , buy it , remove head unit from dash , unplug the blue fakra plug from the back of the head unit (this is the cable that goes to the roof) , plug the "Trimble GPS" fakra end into the head unit , and run cable maybe to glovebox , or behind front pillar - depending where the best signal is.
trimble on eBay (u can get cheaper search "gps fakra" - Trimble will be better
Trimble Active GPS antenna Fakra C-Jack for Audi VW RNS2 MFD2 _ MAGNET MOUNT | eBay